Senju Metal Industry Co., Ltd.

Other

Matsushita Electric Industrial Co., Ltd.

Panasonic Corporation

Kunihito Takaura

Toshihiko Taguchi

Masahiko Hirata

Takashi Nagashima

Hisahiko Yoshida

Kaichi Tsuruta

Hiroji Noguchi

Hiroshi Takahashi

Hiroshi Kawanakago

Setsuko Tadokoro

Takashi c/o Matsushita Elec Ind Co Ltd Nagashima

Masahiko c/o Matsushita Elec Ind Co Ltd Hirata

Hisahiko c/o Matsushita Elec Ind Co Ltd Yoshida

A solder paste using a Sn&#x2014;Ag base, Sn&#x2014;Cu base, or similar alloy powder has a high melting point, so it causes thermal damage to electronic devices. Sn&#x2014;Ag&#x2014;In base lead-free solder alloys having a low melting temperature have been studied, but they are difficult to use because they cause much occurrence of chips standing up during reflow. The present invention forms a solder paste by separating a Sn&#x2014;Ag&#x2014;In base lead-free solder into first and second solder alloy powders for which the difference in their peak temperatures measured by differential thermal analysis is at least 10&#xb0; C. and blends the mixed powders with a flux.

Solder paste

A solder paste comprising a powder of a Zn-containing Sn-based, lead-free solder mixed with an activator-containing rosin-based flux to which 0.5-10.0 wt % of isocyanuric acid or a haloalkyl ester thereof is added can prevent the formation of solder balls and voids during reflow soldering and exhibit good solderability. A solder paste comprising a powder of an Ag- or Zn-containing Sn-based, lead-free solder mixed with an activator-containing rosin-based flux to which 0.01-10.0 wt % of a salicylamide compound also does not exhibit a change in viscosity and exhibits good solderability.

A lead-free solder paste comprises an Sn&mdash;Zn based lead-free solder powder mixed with a flux. The flux contains at least one aromatic hydroxycarboxylic acid selected from the group consisting of aromatic carboxylic acids having one hydroxyl group in a meta position (such as 3-hydroxy-2-methylbenzoic acid) and aromatic carboxylic acids having at least two hydroxyl groups (such as dihydroxynaphthoic acid or dihydroxybenzoic acid) in an amount of 0.1-10.0 mass %. The flux may further include 0.5-20 mass % of an aliphatic hydroxy carboxylic acid (such as hydroxyoleic acid).

A solder paste having a powder of a Zn-containing solder alloy such as an Sn&mdash;Zn based alloy in admixture with a soldering flux such as a rosin flux is improved by adding from 0.1% to 5.0% by weight of a glycidyl ether compound such as alkyl, alkenyl, or aryl glycidyl ether. The improved solder paste has increased resistance to aging and to concomitant deterioration in solderability caused by reaction of Zn in the solder alloy with ingredients in the flux and has a substantially extended shelf life.

Lead-free zinc-containing solder paste

In order to prevent aging of an Sn--Zn system alloy solder paste, 0.5-5% by weight of a compound obtained by adding an ethylene oxide to cyclohexylamine, preferably together with 0.5-5% by weight of a polyoxyethylene alkylamine is added to a flux of said solder paste.

Growing community of inventors

Mouka, Japan

Kunihito Takaura